The present invention relates to a shock absorber for absorbing a shock of a moving member in case the moving member, such as work, is transferred from a moving state to a stopping state.
In a conventional shock absorber, oil is used, as shown in FIG. 8 of Japanese Patent Application No. 2000-153832 (corresponding U.S. patent application Ser. No. 09/571,593). Thus, there is a disadvantage of oil stain due to the oil leakage and oozing out of oil.
In order to eliminate the above disadvantage, a shock absorber using air has been invented, as shown in, for example, FIG. 1 through FIG. 3 of Japanese Patent Application No. 2000-153832.
FIGS. 7 through 9 generally correspond to FIGS. 1 through 3 of Japanese Patent Application No. 2000-153832, and as an example of a prior shock absorber, a shock absorber in FIGS. 7 through 9 will be briefly explained based mainly on operations thereof. From a state shown in FIG. 7, a moving member W is moved rightward, and a piston shaft 102 pressed by the moving member W slides in a piston bearing 101a to be displaced rightward, so that a piston 103 provided integrally with the piston shaft 102 compresses air in a cylinder 101 (refer to FIG. 8).
In this case, in order to prevent a space between a left end side of the piston 103 and an inner wall of a left side of the cylinder 101 from becoming a vacuum state, air flows to the left side of the piston 103 through an air extracting hole 109.
As shown in FIG. 8, air compressed by the piston 103 passes through a first air passage 116, and flows in an arrow direction for a flow quantity determined by a flow quantity control valve formed of a flow quantity control shaft 113b and a flow quantity control shaft hole 114 of a speed controller section B, and air flows backward to outside or a compressed air tank, not shown, through a second air passage 117 and a tube 118.
Furthermore, when the piston 103 reaches an inner end portion of the cylinder 101 such that the right end of the piston 103 abuts against a cylinder wall 106 or a contact 105 abuts against a left end of the piston bearing 101a, the moving member W stops while receiving cushions of air and a compressing coil spring 108.
When the pressing force of the moving member W against the piston 102 is removed, the piston 103 starts moving leftward by a reactive force of the compression coil spring 108 and an air pressure from the compression air tank (refer to FIG. 9).
In this case, as shown in FIG. 9, since air in the second air passage 117 opens a check valve 115 by resisting against the pressing force of the compression coil spring 115a such that the air in the second air passage 117 is directly sent to the first air passage 116, a large quantity of air flows in a short time regardless of the flow quantity of air determined by a slit formed by the flow quantity controlling shaft 113b and the flow quantity controlling shaft hole 114. Thus, the piston 3 is quickly displaced leftward to restore to the state shown in FIG. 7.
Incidentally, reference numeral 116a denotes a groove connecting the first air passage 116 and an air chamber 115b, and the check valve 115 can be opened without compressing air in the air chamber 115b. 
In the shock absorber using air as described above, as compared to the shock absorber using oil, there might be a case that the force of absorbing a shock is insufficient in order to absorb a movement of the detecting member, and in this case, a larger-scaled shock absorber has to be used.
In view of the foregoing, an object of the invention is to provide a shock absorber, in which a force of absorbing a shock is increased to be equivalent to the shock absorber using oil, and air inside the shock absorber is airtightly confined irrespective of outside air, such that dustproof and waterproof functions are made perfect, and the shock absorber can be used in a clean room.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned objects, the present invention provides a shock absorber, which comprises: a cylinder having a cylinder chamber; a piston bearing integrally formed at one end of the cylinder to be arranged coaxially therewith; a piston slidably provided in the cylinder chamber and having a piston shaft including a distal end projecting from the piston bearing; a flow quantity control valve disposed at the other side of the cylinder; a check valve disposed at the other side of the cylinder; a through hole bored through a piston to penetrate from a piston bearing side to a side located opposite to the piston bearing; and valve means provided in the through hole. The piston shaft slidably moves in the piston bearing when the distal end thereof is pressed by a moving member, and the piston compresses air in the cylinder chamber when the piston is pushed toward the other end of the cylinder, so that a portion of the cylinder chamber located at a side of the piston bearing is made into a vacuum state.
The flow quantity control valve is provided for controlling a quantity of air flowing between the cylinder chamber and an outside of the cylinder chamber, to thereby control a force of absorbing a shock in case the piston compresses air in the cylinder chamber. The check valve is opened only when air is fed from the outside of the cylinder into the cylinder chamber in case the piston returns to an original position after the piston compressed air in the cylinder chamber, to thereby send a large amount of air rapidly. The valve means opens and closes in accordance with a movement of the piston in the cylinder chamber, to thereby increase the force of absorbing the shock.
Also, the shock absorber includes air storing means provided for storing air passing through the flow quantity control valve outside the cylinder chamber, and the air storing means is sealed to thereby increase the force of absorbing the shock. The sealed air storing means allows air in the shock absorber to be airtightly confined therein. Further, the air storing means has a capacity which is variable.
In addition, in the shock absorber as stated above, the valve means is formed of first valve means and second valve means. The first valve means is opened in case the piston approaches an end surface of the cylinder opposite to the side of the piston bearing, and the first valve means includes a valve operation shaft slidably abutting against the end surface of the cylinder opposite to the side of the piston bearing to thereby open the first valve means. The second valve means is opened only when the piston is moving toward an end surface of the cylinder in the side of the piston bearing.
Also, instead of having the sealed air storing means inside the shock absorber, the shock absorber can be provided with an air passage passing through the flow quantity controlling valve and extending between the cylinder chamber and an outside of the shock absorber. A portion of the air passage projecting outside the shock absorber can be connected to an external air chamber, or a compressed air tank.